Inheritance, Variation & Evolution
What's covered
Key facts
Classification (Edexcel)
A scientific name consists of two parts: the genus and the species.
DNA and the Genome
In DNA, A pairs with T and C pairs with G.
Genetic Engineering
Genetic engineering raises genuine ethical concerns: modified genes can spread to wild plants, for example through cross-pollination.
Inheritance
A carrier of a recessive disease has one disease allele but shows no symptoms (heterozygous, e.g. Ff for cystic fibrosis).
Inherited Diseases
Cystic fibrosis is autosomal recessive because it is caused by a recessive allele on a non-sex chromosome (CFTR on chromosome 7).
Natural Selection and Evolution
Antibiotic resistance in bacteria is a modern example of natural selection: resistant bacteria survive antibiotic exposure and pass on the resistance gene.
Speciation
Allopatric speciation involves three steps: isolation, different selection pressures, then genetic divergence.
Variation
Continuous variation shows a smooth range of values with no distinct categories, e.g. height, mass.
Classification (Edexcel)
Linnaeus is credited with creating the binomial naming system.
DNA and the Genome
Chromosomes are the structures inside the nucleus that carry the DNA molecules.
Practice questions with answers
A taste of the 89 questions in this topic, answers marked. Sign up to practise the full set with spaced repetition.
Who proposed the five-kingdom classification system?
- •Carl Linnaeus
- •Carl Woese
- •Charles Darwin
- ✓Robert Whittaker
What is a gene?
- ✓A section of DNA that codes for a specific protein.
- •A sequence of amino acids that forms one specific protein.
- •A whole chromosome that carries many different alleles.
- •The complete set of DNA contained in a single cell.
What is a GM crop?
- •Crop bred over many generations
- •Crop given mineral supplements
- •Crop sprayed with growth hormone
- ✓Crop with altered DNA for improved traits
In a cross between two heterozygous tall plants (Tt × Tt), what is the expected ratio of tall to short offspring?
- •1 tall : 1 short
- •1 tall : 3 short
- ✓3 tall : 1 short
- •All tall plants
Why is cystic fibrosis autosomal recessive?
- •Autosomal recessive means dominant alleles on the sex chromosome.
- ✓Caused by a recessive allele on a non-sex chromosome.
- •It is caused by an extra chromosome rather than a faulty gene.
- •It only affects people with type A blood: carriers differ.
What is natural selection?
- ✓Better-adapted individuals are more likely to survive, breed and pass on alleles
- •Humans choose organisms with desired traits and breed them over many generations.
- •Organisms develop useful features during their lifetime and pass these on to offspring.
- •Organisms mutate in response to the environment so that they can survive.
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